It is proposed that we continue our experiments as follows: Finish studies on the ability of the L5178Y S/S variant to complete the restoration of X-ray-induced DNA strand breaks as a function of cycle position following low doses of X-rays (25-500 rads); extend similar investigations to the Chinese hamster ovary cell line and then begin to explore the responses from individual chromosomes of that cell line. Explore further, the response of the L5178Y S/S variant to X-rays as a function of hypo- and hyperthermic pre- and post-irradiation temperatures. Attempt a preliminary identification of the DNA synthetic patterns of the L5178Y S/S variant at defined stages of the cell cycle.